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National Aeronautics and Space Administration
www.nasa.gov
Synthesis and properties of cross-linked
polyamide aerogels
Jarrod Williams
Mary Ann Meador
Linda McCorkle
NASA Glenn Research Center21000 Brookpark Rd, Cleveland, OH 44135
https://ntrs.nasa.gov/search.jsp?R=20150023054 2020-03-01T19:40:26+00:00Z
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Overview
• Aerogel Basics/Applications
• Relevant prior work involving polyamides and polyimides
• Hurdles– The first step growth polyamide aerogel
• Optimization of completely aromatic systems
• Results– Density
– Porosity
– Surface area
– Compressive strength
– Dielectric measurements
• Conclusions/Acknowledgements
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Typical monolithic silica aerogels
What are aerogels?
• Highly porous solids made by drying a wet gel
without shrinking
• Pore sizes extremely small (typically 10-40
nm)—makes for very good insulation
• 2-4 times better insulator than fiberglass under
ambient pressure, 10-15 times better in light
vacuum
• Invented in 1930’s by Prof. Samuel Kistler of
the College of the Pacific
Sol Gel Aerogel
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Potential applications
Optically transparent antennae for use
with solar components
Flexible Insulation
for spacesuits
Low dielectric antenna substrates
Durable/Fire
resistant
structural
insulation
Insulation for crucial
mechanical components
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Basic polymer aerogel processing
Cross-linker
Syringe Mold
Solvent
Exchange
(acetone or
Ethanol)
Supercritical
CO2 drying
Polymer
solution Cross-
linked gel
Solvent
exchanging
in ethanol
Solvent
removed/
Aerogel
4 STEPS1. Polymer solution prepared
2. Cross-linking agent is added and the
mixture is poured into a mold
3. The resulting gel is solvent exchanged
with a SCF compatible solvent such as
ethanol
4. The solvent is then removed using an
SCF such as carbon dioxide
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Polymer Aerogels vs. Silica Aerogels
6
Recently developed polyurea
and polyimide aerogels have
Young’s moduli that are
orders of magnitude larger
than traditional silica aerogel.
The motivation behind
investigating stepgrowth
polyamide aerogels is to see
if we can obtain species that
are even stronger.
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Early literature involving polyamide aerogels
+
Desmodur RE (TIPM) Trimesic acid (TMA)
90°C, anh. DMF
(-CO2)
TIPM
TMA
TIPMTIPM
• Made via non-conventional
amide forming methodology
• No control over chain length
• Glove box conditions
• Long reaction times
• High temperature
• Attempts at polymer chain
formation lead to precipitation
Leventis et. al. J. Mater. Chem., 2011, 21, 11981
X
90°C, anh DMF
(-CO2)
.........
Precipitate
......... X
X,Y=Aromatic
Y
X Y YX
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Polyimides as a Model for Polyamide Aerogels
Comparable to polyimide aerogel
processes.
Similarities include:
1. Analogous polymerization between
diamines and diacid chlorides
2. Crosslinking through the use of a
trifunctional monomer (higher
degrees of functionality are also
possible)
3. Quick reaction times
4. No glove box required
5. Low temperature reaction conditions
6. Polymer chains that stay in solution
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Cross-linked Polyamides (general)
Polymer 41 (2000) 8487-8500
Niesten et. al.
Aromatic amines do not
require a catalyst
Aliphatic amines do require a
catalyst (Et3N)
0°C, NMP
n=20-30
0°C, NMP
X
X=Aromatic
Y=Aromatic or
Aliphatic
Y
X Y YX
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Potential features of polyamide aerogels
• Wide range of properties
– From flexible/soft to rigid/strong
– Hydrophobic/Hydrophilic
– Colorless (maybe translucent/clear)
– Low cost (monomers, cross-linker)
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Completely aromatic systems
Advantages: 1. No catalyst required (NMP
complexes with HCl)
2. Amine end caps make mixture
stable to moisture indefinitely.
3. Reaction mixtures remain
homogenous
4. Reactions undergo reliable
gelation (more user friendly than
acid chloride endcaps)
5. Control over rigidity
One problem
remained……….
DMBZ
Isophthaloyl chloride
[
]n
NMP, Room temperature
NMP, 0°C
Cross-linked PolyamideNetwork
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Optimized vs. Non-optimized Systems
Left two figures:
Polyamide
aerogels before
procedure
optimization.
Right two figures:
Three different
polyamide
aerogels (and
SEMs) made via
and optimized
procedure.
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Optimization of Polyamide Aerogels
• To minimize distortion, the following reaction
parameters were examined and optimized
– Reaction and Cross-linking temperature
– Stirring time/Stirring speed
– Concentration of solutions
– Cross-link density
– Order and manner of addition of the reactants
– Monomer species
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Samples From Optimized Procedure
Isophthaloyl chloride, terephthaloyl chloride, m-phenylene
diamine, 0.10g/cm3, 93% porous, 192 m2/g.
Terephthaloyl chloride, 0.33g/cm3, 77% porous, 384
m2/g.
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Monomers
1,3,5-Benzenetricarbonyl
trichloride (1,3,5-BTC)
Isophthaloyl chloride
(IPC)Terephthaloyl chloride
(TPC)m-phenylenediamine
(mPDA)
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Aerogel Synthesis
16
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5.0
7.5
10.0
0
50
100
2030
40
Solid
concentr
ation, %
p-A
cid c
hlo
ride, %
Repeat units, n
Experimental design study
• Face-centered
central composite
design
• 15 different data
points to model full
quadratic equation
• 4 repeats of the
center point to
assess error
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Results: Density
• Density increases as
the fraction of the para
substituted acid
chloride increases.
• Density increases as
the concentration of
solids in the gel
increases.
• n-value or length of the
polymer chains, is not
a significant factor for
density
• Standard
deviation=0.016
• R2=0.98
0.0
0.1
0.2
0.3
0.4
0
20
406080100
5678910
Density,
g/c
m3
TP
C c
onc.
, %
Polymer conc., w/w %
n = 20
n = 40
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Results: Porosity
• Porosity decreases as
the fraction of the para
substituted acid
chloride increases.
• Porosity decreases as
the concentration of
solids in the gel
increases.
• n-value of the polymer
chains is not a
significant factor for
porosity.
• SD=1.26
• R2=0.98
70
75
80
85
90
95
100
105
020
4060
80100
67
89
10
Poro
sity,
%
TPC conc., %
Polymer conc., wt%
n = 20
n = 40
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Surface area
• All three variables
significant
• Data was log
transformed before
fitting to normalize
data
• S.D. = 36.64
• R2=0.88
20
0
100
200
300
400
500
0
25
50
75
100
56
78
9
Surf
ace
are
a, m
2/g
TPC c
onc.
, %
Polymer conc., %
3D Graph 1
n=20
n=40
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Dielectric and Loss Tangent
21
1.2
1.4
1.6
020
4060
80100
56
78
910R
ela
tive d
iele
ctric
const
ant
TPC conc., %Polymer conc., %
3D Graph 1
0.000
0.005
0.010
0.015
0.020
0.025
0
20
40
6080
100
56
78
9
Loss
tangent
TPC c
onc.
, %
Polymer conc., %
3D Graph 1
n = 20
n = 40
2D Graph 1
Density, g/cm3
0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36
Rela
tive d
iele
ctr
ic c
onsta
nt
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
2D Graph 1
Density, g/cm3
0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36
Loss t
ang
en
t
0.000
0.005
0.010
0.015
0.020
0.025
0.030
SD=0.042, R2=0.92SD=0.0017, R2=0.93
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Compressive Strength
22
0
1
2
3
4
5
6
0
20
4060
80100
56
78
910
Str
ess a
t 10%
str
ain
, M
Pa
TPC
con
c., %
Polymer conc., %
3D Graph 2
2D Graph 2
Density, g/cm3
0.05 0.06 0.070.080.09 0.2 0.3 0.40.1
Str
ess
at 1
0% s
trai
n, M
Pa
0.1
1
10
SD=0.16, R2=0.90
2D Graph 2
Strain, %
0 10 20 30 40 50 60 70 80
Str
ess
, M
Pa
0
2
4
6
8
10
12
14
16
18100% TPC
50% IPC/50% TPC
100% IPC
2D Graph 1
Polymer conc., w/w %
4 5 6 7 8 9 10 11
Str
ess a
t 1
0%
str
ain
, M
Pa
0.1
1
10
100 % IPC
50 % IPC/50% TPC
100% TPC
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Young’s Modulus
23
2D Graph 1
Polymer conc., w/w %
4 5 6 7 8 9 10 11
Mo
dulu
s,
MP
a
1
10
100
1000
100 % IPC
50 % IPC/50% TPC
100% TPC
(log standard deviation=0.25, R2=0.79)1. Guo et. al. ACS. Appl. Mater. Interfaces, 2011, 3,
546-552.
2. Leventis et. al. J. Mater. Chem. 2011, 21, 11981-
11986.
3. Fricke et. al. J. Non-Cryst. Solids, 1988, 100
169-173.
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Conclusions/Summary
• A simple procedure for the fabrication of polyamide
aerogels has been developed and optimized
• A series of polyamide aerogels were produced that
having densities ranging from 0.06g/cm3 to 0.3g/cm3,
high porosities (77-93% porous), and surface areas
as high as 426m2/g
• Diverse properties arise through controlling monomer
types, stoichiometry and weight percent solids
• Remaining work
– Examine new monomer species
– Experiment with different crosslinking methodologies
– N-alkylate for hydrophobicity
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Acknowledgements
NASA Glenn
1. Dr. Mary Ann Meador
2. Stephanie Vivod
3. Baochau Nguyen
4. Heidi Guo
5. Linda McCorkle
6. Dan Haas
7. Dan Scheiman
The NASA Postdoc Program and Oak
Ridge associated Universities (ORAU)
NASA Glenn Center Director’s Special
Project Fund
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